1. The Field of the Invention
The present invention relates the manufacture of semiconductor devices. More particularly, the present invention relates to a semiconductor wafer having semiconductor devices thereon, the semiconductor wafer having a substrate subjected to a series of processing steps for forming silicide films on monocrystalline amorphous, or polycrystalline silicon, the processing steps serving to reduce interfacial failures on the wafer due to agglomeration within the silicide films during high temperature anneal processing steps.
2. The Relevant Technology
As is well known in the art, polycrystalline silicon (polysilicon) is a preferred material for gate electrodes in MOSFET structures. Polysilicon is advantageous over metal gate electrodes because it can withstand much higher subsequent processing temperatures before eutectic temperatures are reached. Polysilicon can be deposited on bulk silicon or SiO.sub.2 using low pressure chemical vapor deposition (LPCVD).
As the drive toward integrating more active devices on a single integrated circuit necessitates the fabrication of increasingly smaller MOSFET structures, the resistance of the MOSFET gate becomes a limiting factor in device speed. As such, it is beneficial to use materials with the lowest possible sheet resistivities for making contact with the polysilicon gate structure. To this end it is well known that refractory metal suicides can be readily formed on polysilicon MOSFET gate structures using conventional semiconductor deposition and annealing techniques. The refractory metal suicides have low sheet resistivities after annealing and also form low resistance ohmic contacts with commonly used interconnect metals. The resistance of the silicide/polysilicon structures and their overall integrity are greatly affected by the manner in which the structures are processed.
Titanium silicide (TiSi.sub.2) has a low sheet resistivity when it has been annealed to a C54 phase. To obtain the desired low resistivities requires high temperature annealing in the range of 700.degree. C.-1100.degree. C. Numerous techniques for creating and annealing TiSi.sub.2 films on MOSFET gate source and drain electrodes are known, and for obtaining the desired low sheet resistivities. The most common of these techniques involves depositing either pure titanium metal, or co-depositing titanium silicide (TiSi.sub.2), with subsequent annealing steps to convert the deposited layer to TiSi.sub.2 in a C54 phase.
The use of TiSi.sub.2 in silicon gate MOSFET fabrication is becoming limited by insufficient process stability at the desired processing temperatures. This instability creates a problem as the trend toward more complex integrated circuits necessitates an increasing number of high temperature processing steps after the deposition and formation of the silicide layer. An unwanted side effect of the high temperature instability of TiSi.sub.2 is caused by agglomeration, which is known to occur during high temperature polysilicon processing. Agglomeration is a build-up of re-crystallized silicon, metal, or dopant grains at either or both of the interfaces of the polysilicon layer, and typically occurs during high-temperature annealing. Although the mechanisms of agglomeration are complex and varied, it is widely accepted that a major contributing factor to agglomeration is the action of polysilicon grain boundaries as rapid diffusion routes for transporting silicon and/or dopant ions which diffuse out from the polysilicon during annealing. Silicon which out-diffuses from the polysilicon layer and then recrystallizes at the TiSi.sub.2 -polysilicon interface can cause severe discontinuities and voids within the TiSi.sub.2 layer, resulting in higher sheet resistivity of the silicide with greater variation in resistivity and a greater number of defects.
As it is known in the art that high-temperature annealing is required to achieve the minimum possible room-temperature resistivity of any given silicide, it is clear that advances are needed which will better control the mechanical and electrical stability of refractory metal silicide films (e.g TiSi.sub.2) during high-temperature silicide formation and annealing. Accordingly, it would be an advance in the art to avoid agglomeration, develop superior sheet resistivity and device speed, and increase thermal stability characteristics in refractory metal silicide films.